PARENT SESSION
Poster Session 32: Biogeochemistry
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Effects of long-term nitrogen amendment on leaf and wood decomposition in northern hardwood forests.
Rothstein, David*,1, Burton, Andrew2, Zak, Donald3, Pregitzer, Kurt2, 1 Michigan State University, E. Lansing, MI2 Michigan Technological University, Houghton, MI3 University of Michigan, Ann Arbor, MI
ABSTRACT- Anthropogenic nitrogen (N) deposition has the potential to alter the storage and cycling of carbon through its effects on the rate of plant litter decomposition. Previous research suggests that N amendments should speed the decay of labile litter and retard the decay of recalcitrant litter. We studied the decay of Acer saccharum (sugar maple) leaf litter and commercial wood sticks decomposed in four northern hardwood forests in Michigan that have received experimental nitrate amendments for 8 years (30 kg N ha-1 y-1). Two of these sites had lower inherent soil N availability compared to the others, as indicated by lower net N mineralization, fine-root N concentration and leaf litter N concentration. We hypothesized that N amendments would stimulate decay of high quality (C:N = 50) leaf litter, and inhibit the decay of poor quality (C:N = 600) wood. Nitrate amendments had no effect on leaf-litter decay at any of the sites. In contrast, wood decay was slowed markedly in fertilized plots (k = -0.11 y-1 ) relative to control plots (k = -0.38 y-1 ) at a single, low-fertility site. Slower decomposition in the fertilized plots at this site was associated with a 90% decline in polyphenol oxidase activity in decomposing wood. In contrast, polyphenol oxidase activity in decaying wood was only weakly affected by fertilization at the other three sites. These results demonstrate that the effects of N amendments on decomposition are both site and substrate specific.
Key words: decomposition, nitrogen deposition